Your computer DVI-I output may not output analog at all. For example: my graphic card has a VGA and a DVI-I connector. I tried connecting my monitor's VGA input to the Card's DVI connector using a VGA-VGA cable and a DVI-VGA adapter, but I couldn't get any image, no matter if I pushed the video input button on the monitor.

Just because you have a female DVI-I (d+a) doesn't necessarily mean that the adapter/dongle/cable you are using support specifically analog connections.

If for instance you attempted to plug a DVI-A into what looks like a DVI-I dual-link (d+a) female connection and you get no output, it is probably because the adapter/dongle/cable you have doesn't actually support analog IO.